I thought I'd read this, but I hadn't. Eric Flint compared this to Theodore Sturgeon's "Thunder and Roses," but this is more of the optimistic side of humanity's future.
A group of aliens see that Earth's Sun is about to go supernova (not sure where science was in regards to stars, but scientists do not believe it could go nova--and definitely not within two hundred years. I read a more recent SF story where this occurred, but I forget whose). So a starship arrives to whisk the inhabitants away. However, they cannot find any. They cover the planet, they look under the ocean, and they even take an elevator through Earth. Nothing.
SPOILER / discussion:
Finally, they realize humanity had already left, using what little technology it had. The aliens admire them, even fear them. Interesting last note to end on. It reminds me a bit of Mike Resnick's note in "Seven Views of Olduvai Gorge."
The power of this tale is how Clarke takes what looks like a traditional disaster tale and turns it on its head. "Oh, no! Humans are all gonna die! ... Oh, wait. They're actually going to thrive." Instead, the aliens themselves need rescuing--perhaps in and out of the narrative.